Nitrogen-containing compounds as additives for silicon-based Li-ion batteries

ABSTRACT

Additives for energy storage devices comprising nitrogen-containing compounds are disclosed. The energy storage device comprises a first electrode and a second electrode, where at least one of the first electrode and the second electrode is a Si-based electrode, a separator between the first electrode and the second electrode, and an electrolyte composition. Nitrogen-containing compounds may serve as additives to the first electrode, the second electrode, and/or the electrolyte, as well as the separator.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

N/A

FIELD

Aspects of the present disclosure relate to energy generation andstorage. More specifically, certain embodiments of the disclosure relateto additives for use in lithium-ion energy storage devices withsilicon-based anode materials.

BACKGROUND

Conventional approaches for battery electrodes may be costly,cumbersome, and/or inefficient—e.g., they may be complex and/ortime-consuming to implement, and may limit battery lifetime.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present disclosureas set forth in the remainder of the present application with referenceto the drawings.

BRIEF SUMMARY

A system and/or method for using nitrogen-containing additive compoundsin lithium-ion energy storage devices with silicon-based electrodematerials, substantially as shown in and/or described in connection withat least one of the figures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the presentdisclosure, as well as details of an illustrated embodiment thereof,will be more fully understood from the following description anddrawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a battery, in accordance with an exampleembodiment of the disclosure.

FIG. 2 is a flow diagram of a lamination process for forming asilicon-dominant anode cell, in accordance with an example embodiment ofthe disclosure.

FIG. 3 is a flow diagram of a direct coating process for forming asilicon-dominant anode cell, in accordance with an example embodiment ofthe disclosure.

FIG. 4 shows cyclic voltammetry (CV) curves of NCM811 cathode-based coinhalf cells with 1 wt % 1,4-Phenylene Diisothiocyanate (PDIST) with avoltage range of 2.0-4.3 V, in accordance with an example embodiment ofthe disclosure.

FIGS. 5A and 5B show the Capacity retention (FIG. 5A) and Normalizedcapacity retention (FIG. 5B) of Si-dominant anode//NCM811 cathode coinfull cells. The cathode used may be: (dotted line)—NCM811 Control,(solid line)—1 wt % 1,4-Phenylene Diisothiocyanate (PDIST)-containingNCM811, in accordance with an example embodiment of the disclosure.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a battery with silicon-dominant anodes, inaccordance with an example embodiment of the disclosure. Referring toFIG. 1 , there is shown a battery 100 comprising a separator 103sandwiched between an anode 101 and a cathode 105, with currentcollectors 107A and 107B. There is also shown a load 109 coupled to thebattery 100 illustrating instances when the battery 100 is in dischargemode. In this disclosure, the term “battery” may be used to indicate asingle electrochemical cell, a plurality of electrochemical cells formedinto a module, and/or a plurality of modules formed into a pack.Furthermore, the battery 100 shown in FIG. 1 is a very simplifiedexample merely to show the principle of operation of a lithium-ion cell.Examples of realistic structures are shown to the right in FIG. 1 ,where stacks of electrodes and separators are utilized, with electrodecoatings typically on both sides of the current collectors. The stacksmay be formed into different shapes, such as a coin cell, cylindricalcell, or prismatic cell, for example.

The development of portable electronic devices and electrification oftransportation drive the need for high-performance electrochemicalenergy storage. Small-scale (<100 Wh) to large-scale (>10 KWh) devicesprimarily use lithium-ion (Li-ion) batteries over other rechargeablebattery chemistries due to their high performance.

The anode 101 and cathode 105, along with the current collectors 107Aand 107B, may comprise the electrodes, which may comprise plates orfilms within, or containing, an electrolyte material, where the platesmay provide a physical barrier for containing the electrolyte as well asa conductive contact to external structures. In other embodiments, theanode/cathode plates are immersed in electrolyte while an outer casingprovides electrolyte containment. The anode 101 and cathode areelectrically coupled to the current collectors 107A and 1078, whichcomprise metal or other conductive material for providing electricalcontact to the electrodes as well as physical support for the activematerial in forming electrodes.

The configuration shown in FIG. 1 illustrates the battery 100 indischarge mode, whereas in a charging configuration, load 109 may bereplaced with a charger to reverse the process. In one class ofbatteries, the separator 103 is generally a film material, made of anelectrically insulating polymer, for example, that prevents electronsfrom flowing from anode 101 to cathode 105, or vice versa, while beingporous enough to allow ions to pass through the separator 103.Typically, the separator 103, cathode 105, and anode 101 materials areindividually formed into sheets, films, or active material coated foils.Sheets of the cathode, separator, and anode are subsequently stacked orrolled with the separator 103 separating the cathode 105 and anode 101to form the battery 100. In some embodiments, the separator 103 is asheet and generally utilizes winding methods and stacking in itsmanufacture. In these methods, the anodes, cathodes, and currentcollectors (e.g., electrodes) may comprise films.

In an example scenario, the battery 100 may comprise a solid, liquid, orgel electrolyte. The separator 103 preferably does not dissolve intypical battery electrolytes such as compositions that may comprise:Ethylene Carbonate (EC), Fluoroethylene Carbonate (FEC), PropyleneCarbonate (PC), Dimethyl Carbonate (DMC), Ethyl Methyl Carbonate (EMC),Diethyl Carbonate (DEC), etc. with dissolved LiBF₄, LiAsF₆, LiPF₆, andLiClO₄ etc. In an example scenario, the electrolyte may comprise Lithiumhexafluorophosphate (LiPF₆) and lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI) that may be used together ina variety of electrolyte solvents. Lithium hexafluorophosphate (LiPF₆)may be present at a concentration of about 0.1 to 4.0 molar (M) andlithium bis(trifluoromethanesulfonyl)imide (LiTFSI) may be present at aconcentration of about 0 to 4.0 molar (M). Solvents may comprise one ormore of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and/orethyl methyl carbonate (EMC) in various percentages. In someembodiments, the electrolyte solvents may comprise one or more of ECfrom about 0-40%, FEC from about 2-40%, and/or EMC from about 50-70%

The separator 103 may be wet or soaked with a liquid or gel electrolyte.In addition, in an example embodiment, the separator 103 does not meltbelow about 100 to 120° C. and exhibits sufficient mechanical propertiesfor battery applications. A battery, in operation, can experienceexpansion and contraction of the anode and/or the cathode. In an exampleembodiment, the separator 103 can expand and contract by at least about5 to 10% without failing, and may also be flexible.

The separator 103 may be sufficiently porous so that ions can passthrough the separator once wet with, for example, a liquid or gelelectrolyte. Alternatively (or additionally), the separator may absorbthe electrolyte through gelling or other processes even withoutsignificant porosity. The porosity of the separator 103 is alsogenerally not too porous to allow the anode 101 and cathode 105 totransfer electrons through the separator 103.

The anode 101 and cathode 105 comprise electrodes for the battery 100,providing electrical connections to the device for the transfer ofelectrical charge in charge and discharge states. The anode 101 maycomprise silicon, carbon, or combinations of these materials, forexample. Typical anode electrodes comprise a carbon material thatincludes a current collector such as a copper sheet. Carbon is oftenused because it has excellent electrochemical properties and is alsoelectrically conductive. Anode electrodes currently used in rechargeablelithium-ion cells typically have a specific capacity of approximately200 milliampere hours per gram. Graphite, the active material used inmost lithium-ion battery anodes, has a theoretical energy density of 372milliampere hours per gram (mAh/g). In comparison, silicon has a hightheoretical capacity of 4200 mAh/g. To increase the volumetric andgravimetric energy density of lithium-ion batteries, silicon may be usedas the active material for the cathode or anode. Silicon anodes may beformed from silicon composites, with more than 50% silicon or more byweight in the anode material on the current collector, for example.

In an example scenario, the anode 101 and cathode 105 store the ion usedfor the separation of charge, such as lithium. In this example, theelectrolyte carries positively charged lithium ions from the anode 101to the cathode 105 in discharge mode, as shown in FIG. 1 for example,and vice versa through the separator 105 in charge mode. The movement ofthe lithium ions creates free electrons in the anode 101 which creates acharge at the positive current collector 1078. The electrical currentthen flows from the current collector through load 109 to the negativecurrent collector 107A. The separator 103 blocks the flow of electronsinside the battery 100, allows the flow of lithium ions, and preventsdirect contact between the electrodes.

While battery 100 is discharging and providing an electric current, theanode 101 releases lithium ions to the cathode 105 via the separator103, generating a flow of electrons from one side to the other via thecoupled load 109. When the battery is being charged, the oppositehappens where lithium ions are released by the cathode 105 and receivedby the anode 101.

The materials selected for the anode 101 and cathode 105 are importantfor the reliability and energy density possible for the battery 100. Theenergy, power, cost, and safety of current Li-ion batteries need to beimproved in order to, for example, compete with internal combustionengine (ICE) technology and allow for the widespread adoption ofelectric vehicles (EVs). High energy density, high power density, andimproved safety of lithium-ion batteries are achieved with thedevelopment of high-capacity and high-voltage cathodes, high-capacityanodes and functionally non-flammable electrolytes with high voltagestability and interfacial compatibility with electrodes. In addition,materials with low toxicity are beneficial as battery materials toreduce process costs and promote consumer safety.

The performance of electrochemical electrodes, while dependent on manyfactors, is largely dependent on the robustness of electrical contactbetween electrode particles, as well as between the current collectorand the electrode particles. The electrical conductivity of siliconanode electrodes may be manipulated by incorporating conductiveadditives with different morphological properties. Carbon black (forexample, SuperP), vapor-grown carbon fibers (VGCF), and a mixture of thetwo have previously been incorporated separately into the anodeelectrode resulting in improved performance of the anode. Thesynergistic interactions between the two carbon materials may facilitateelectrical contact throughout the large volume changes of the siliconanode during charge and discharge. These contact points facilitate theelectrical contact between anode material and current collector tomitigate the isolation (island formation) of the electrode materialwhile also improving conductivity in between silicon regions.

State-of-the-art lithium-ion batteries typically employ agraphite-dominant anode as an intercalation material for lithium.Silicon-dominant anodes, however, offer improvements compared tographite-dominant Li-ion batteries. Silicon exhibits both highergravimetric (4200 mAh/g vs. 372 mAh/g for graphite) and volumetriccapacities (2194 mAh/L vs. 890 mAh/L for graphite). In addition,silicon-based anodes have a low lithiation/delithiation voltage plateauat about 0.3-0.4V vs. Li/Li+, which allows it to maintain an opencircuit potential that avoids undesirable Li plating and dendriteformation. While silicon shows excellent electrochemical activity,achieving a stable cycle life for silicon-based anodes is challengingdue to silicon's large volume changes during lithiation anddelithiation. Silicon regions may lose electrical contact from the anodeas large volume changes coupled with its low electrical conductivityseparate the silicon from surrounding materials in the anode.

In addition, the large silicon volume changes exacerbate solidelectrolyte interphase (SEI) formation, which can further lead toelectrical isolation and, thus, capacity loss. Expansion and shrinkageof silicon particles upon charge-discharge cycling causes pulverizationof silicon particles, which increases their specific surface area. Asthe silicon surface area changes and increases during cycling, SEIrepeatedly breaks apart and reforms. The SEI thus continually builds uparound the pulverizing silicon regions during cycling into a thickelectronic and ionic insulating layer. This accumulating SEI increasesthe impedance of the electrode and reduces the electrode electrochemicalreactivity, which is detrimental to cycle life. Therefore, siliconanodes require a strong conductive matrix that (a) holds siliconparticles in the anode, (b) is flexible enough to accommodate the largevolume expansion and contraction of silicon, and (c) allows fastconduction of electrons within the matrix.

Therefore, there is a trade-off among the functions of active materials,conductive additives, and polymer binders. The balance may be adverselyimpacted by high energy density silicon anodes with low conductivity andhuge volume variations described above. Polymer binder(s) may bepyrolyzed to create a pyrolytic carbon matrix with embedded siliconparticles. In addition, the polymers may be selected from polymers thatare completely or partially soluble in water or other environmentallybenign solvents or mixtures and combinations thereof. Polymersuspensions of materials that are non-soluble in water could also beutilized.

As the demands for both zero-emission electric vehicles and grid-basedenergy storage systems increase, lower costs and improvements in energydensity, power density, and safety of lithium (Li)-ion batteries arehighly desirable. Enabling the high energy density and safety of Li-ionbatteries requires the development of high-capacity, and high-voltagecathodes, high-capacity anodes, and accordingly functional electrolyteswith high voltage stability, interfacial compatibility with electrodesand safety.

A lithium-ion battery typically includes a separator and/or electrolytebetween an anode and a cathode. In one class of batteries, theseparator, cathode, and anode materials are individually formed intosheets or films. Sheets of the cathode, separator, and anode aresubsequently stacked or rolled with the separator separating the cathodeand anode (e.g., electrodes) to form the battery. Typical electrodesinclude electro-chemically active material layers on electricallyconductive metals (e.g., aluminum and copper). Films can be rolled orcut into pieces which are then layered into stacks. The stacks are ofalternating electro-chemically active materials with the separatorbetween them.

Si is one of the most promising anode materials for Li-ion batteries dueto its high specific gravimetric and volumetric capacity (discussedabove), and low lithiation potential (<0.4 V vs. Li/Li⁺). Cathodematerials may include Lithium Nickel Cobalt Manganese Oxide (NMC (NCM):LiNi_(x)Co_(y)Mn_(z)O₂, x+y+z=1); Lithium Iron Phosphate (LFP:LiFePO₄/C); Lithium Nickel Manganese Spinel (LNMO:LiNi_(0.5)Mn_(1.5)O₄); Lithium Nickel Cobalt Aluminium Oxide (NCA:LiNi_(a)Co_(b)Al_(c)O₂, a+b+c=1); Lithium Manganese Oxide (LMO:LiMn₂O₄); and Lithium Cobalt Oxide (LCO: LiCoO₂).

Among the various cathodes presently available, layered lithiumtransition-metal oxides such as Ni-rich LiNi_(x)Co_(y)Mn_(z)O₂ (NCM,0≤x, y, z<1) or LiNi_(x)Co_(y)Al_(z)O₂ (NCA, 0≤x, y, z<1) are promisingones due to their high theoretical capacity (˜280 mAh/g) and relativelyhigh average operating potential (3.6 V vs Li/Li⁺). In addition toNi-rich NCM or NCA cathode, LiCoO₂ (LCO) is also a very attractivecathode material because of its relatively high theoretical specificcapacity of 274 mAh g⁻¹, high theoretical volumetric capacity of 1363mAh cm⁻³, low self-discharge, high discharge voltage, and good cyclingperformance. Coupling Si anodes with high-voltage Ni-rich NCM (or NCA)or LCO cathodes can deliver more energy than conventional Li-ionbatteries with graphite-based anodes, due to the high capacity of thesenew electrodes. However, both Si-based anodes and high-voltage Ni-richNCM (or NCA) or LCO cathodes face formidable technological challenges,and long-term cycling stability with high-Si anodes paired with NCM orNCA cathodes has yet to be achieved.

For anodes, silicon-based materials can provide significant improvementin energy density. However, the large volumetric expansion (e.g., >300%)during the Li alloying/dealloying processes can lead to disintegrationof the active material and the loss of electrical conduction paths,thereby reducing the cycling life of the battery. In addition, anunstable solid electrolyte interphase (SEI) layer can develop on thesurface of the cycled anodes and leads to an endless exposure of Siparticle surfaces to the liquid electrolyte. This results in anirreversible capacity loss at each cycle due to the reduction at the lowpotential where the liquid electrolyte reacts with the exposed surfaceof the Si anode. In addition, oxidative instability of the conventionalnon-aqueous electrolyte takes place at voltages beyond 4.5 V, which canlead to accelerated decay of cycling performance. Because of thegenerally inferior cycle life of Si compared to graphite, only a smallamount of Si or Si alloy is used in conventional anode materials.

The cathode (e.g., NCM (or NCA) or LCO) usually suffers from inferiorstability and a low capacity retention at a high cut-off potential. Thereasons can be ascribed to the unstable surface layer's gradualexfoliation, the continuous electrolyte decomposition, and thetransition metal ion dissolution into electrolyte solution; furthercauses for inferior performance can be: (i) structural changes fromlayered to spinel upon cycling; (ii) Mn- and Ni-dissolution giving riseto surface side reactions at the graphite anode; and (iii) oxidativeinstability of conventional carbonate-based electrolytes at highvoltage. The major limitations for LCO cathodes are high cost, lowthermal stability, and fast capacity fade at high current rates orduring deep cycling. LCO cathodes are expensive because of the high costof Co. Low thermal stability refers to an exothermic release of oxygenwhen a lithium metal oxide cathode is heated. In order to make good useof Si anode//NCM or NCA cathode, and Si anode//LCO cathode-based Li-ionbattery systems, the aforementioned barriers need to be overcome.

As discussed above, Li-ion batteries are being intensively pursued inthe electric vehicle markets and stationary energy storage devices. Tofurther improve the cell energy density, high-voltage layered transitionmetal oxide cathodes, examples including Ni-rich (e.g. NCA, NCM),Li-rich cathodes, and high capacity and low-voltage anodes, such as Si,Ge, etc may be utilized. However, the performance deterioration of fullcells, in which these oxides are paired with Si or other high capacityanodes, increases markedly at potentials exceeding 4.30 V, limitingtheir wider use as high-energy cathode materials. Although a higher Nicontent provides a higher specific capacity for Ni-rich NCM or NCAcathodes, it involves surface instability because of the unstable Ni⁴⁺increase during the charging process. As it is favorable to convert theunstable Ni⁴⁺ into the more stable Ni³⁺ or Ni²⁺, Ni⁴⁺ triggers severeelectrolyte decomposition at the electrode/electrolyte interface,leading to the reduction of Ni⁴⁺ and the oxidative decomposition of theelectrolytes. Electrolyte decomposition at the electrolyte/electrodeinterface causes the accumulation of decomposed adducts on the NCMcathode surface. This hinders Li+ migration between the electrolyte andelectrode, which in turn results in the rapid fading of the cyclingperformance. Thus the practical integration of a silicon anode in Li-ionbatteries faces challenges such as large volume changes, unstablesolid-electrolyte interphase, electrolyte drying out, etc.

Attempts for improving the cathode surface properties, such asthrough-surface coating, surface doping, and the use of electrolyteadditives that effectively mitigate electrolyte decomposition at theinterface, have been attempted. Most of these attempts are based on thecathode-electrolyte interface (CEI) concept, which does not permitelectron-transfer reactions, but allows Li⁺ migration between theelectrode and electrolyte. However, without negative impacts on theanode, electrolyte, and battery manufacturing procedures or design,adding a cathode additive may be an efficient, cost-effective andpractically feasible strategy to overcome the barriers of layeredcathode materials and improve the full cell performance.

One strategy for overcoming these barriers includes exploring newelectrolyte or electrode additives in order to make good use of Sianode//NCM or NCA cathode-, and Si anode//LCO cathode-based full cells.Such additives should be able to form a uniform, stable SEI layer on thesurface of Si anodes. This layer should have low impedance and beelectronically insulating, but ionically conductive to Li-ion.Additionally, the SEI layer formed by the additive should have excellentelasticity and mechanical strength to overcome the problem of expansionand shrinkage of the Si anode volume. On the cathode side, the idealadditives should be oxidized preferentially to the solvent molecule inthe bare electrolyte, resulting in a protective cathode electrolyteinterphase (CEI) film formed on the surface of the Ni-rich NCM (or NCA)and LCO cathodes. At the same time, it should help alleviate thedissolution phenomenon of transition metal ions and decrease surfaceresistance on the cathode side. In addition, additives could helpimprove the physical properties of the electrolyte such as ionicconductivity, viscosity, and wettability.

Thus incorporation of functional additives may help modify the surfacechemistry, circumvent the massive volume change and initial capacityloss due to the continuous electrolyte decomposition in high capacityand reactive electrodes, such as Si anodes, and/or Ni-rich NCA or NCMcathodes. For Si anodes, the expansion and contraction of silicon causesthe surface area to change. Suitable reducible or oxidizable electrolyteadditives are expected to modify the SEI or CEI interphases,respectively, in Li-ion batteries, thus altering and tuning theircomposition and escorting the corresponding electrochemical properties,such as cycle life, rate capability, energy/power densities, etc. Afurther strategy for improving battery properties is to modify theseparator, which can, e.g., improve cycle performance.

In the present disclosure, nitrogen-containing compounds are describedfor use as additives for electrodes and/or in the electrolytecomposition. Also described in the present disclosure, is the use ofnitrogen-containing compounds to modify the separator to preparedifferent types of functional separators to improve the cycleperformance of Li-ion batteries or Li-metal batteries.

There are two important points in controlling the SEI production; one isthe timing of the SEI formation (additive decomposition) and the otheris the morphology of the SEI (thickness, Li-ion conductivity, andcomponents). Nitrogen-containing compounds have a reduction potentialwhich enables the formation of a characteristic SEI with dense and lowimpedance. Battery performance is significantly influenced by the SEIthickness and components, which are solely determined by the structureof the additives.

The reactivity of additives assists with modification of the SEI layercomposition and improves the SEI stability on the surface of Si anodes,which permits effective surface passivation of the anode, increase SEIrobustness and structural stability of the silicon anodes. At the sametime, the additives disclosed herein can provide high voltage stabilityof cathodes by forming a stable passivation layer on the surface of thecathode. This can mitigate parasitic reactions occurring on the surfaceof the cathode, leading to minimized electrolyte decomposition, loss ofactive Li, and impedance rise on the electrode/electrolyte interface.The additives also assist with the formation of a stable SEI layer andpassivation layer on the surfaces of Si-containing anodes andhigh-voltage cathodes, respectively, and increase the oxidationstability of electrolytes. Full cells may achieve improved cycleperformance and enhanced energy density. Also, since silicon anodes havea continually changing surface, the additives may help to quickly createa passivating thin layer that helps prevent a thicker layer fromforming.

Cathode materials are also still facing some fundamental challenges,such as irreversible phase transition from hexagonal through cubic torock salt structure, mechanical cracking of the secondary particlestructure, electrolyte depletion that is often accompanied by impedanceincrease and volumetric swelling of the batteries, as well as gelationof cathode slurry in the slurry-making process.

Among the various Li-ion battery cathode materials, Ni-rich layeredlithium transition metal oxides are promising cathode materials for thenext generation high energy density lithium-ion batteries due to theirrelatively modest volume change, high specific capacity, and goodthermal stability. However, high Ni content leads to severe sidereactions at the cathode/electrolyte interface, coupled with mechanicaldisintegration significantly degrading the electrochemical performanceand safety. Several strategies have been explored to overcome theseissues, such as cation doping for stabilizing the cathode material'slattice structure, surface coating for protecting cathode particles fromparasitic reactions with the electrolyte components, synthesizingconcentration-gradient or core-shell structures with high Ni contentcore for stabilizing the material's surface chemistry, as well as usingelectrolyte additives for chemically trapping the released oxygen.

Without negative impacts on the anode, electrolyte, and the batterymanufacturing procedures or design, adding a cathode additive asdescribed herein may be an efficient, cost-effective and practicallyfeasible strategy to overcome the barriers of layered cathode materialsand improve the full cell performance. In one embodiment, this may beachieved by placing a coating onto cathode active material powders sothat the cathode powders could be a drop-in replacement in theelectrode.

To overcome the current obstacles associated with developing high-energyfull-cells with Si-based anodes, the next generation of electrode orelectrolyte additives are described herein. These additives may helpmodify cathode surfaces, forming stable CEI layers, or may form astable, electronically insulating but ionically conducting SEI layer onthe surface of Si anodes. These additives may increase theelectrochemical stability of Li-ion batteries when cycled at highervoltages and help with the calendar life of the batteries. In addition,to alleviate battery safety concerns, these additives may impartincreased thermal stability to the organic components of theelectrolyte, drive a rise in the flash point of the electrolyteformulations, increase the flame-retardant effectiveness and enhance thethermal stability of SEI or CEI layers on the surface of electrodes.Further, the additives may produce one or more of the followingbenefits: increased cycle life, increased energy density, increasedsafety, increased thermal stability of the electrolyte, enhancedhigh-temperature performance of the cells, decreased electrolyteconsumption, and/or decreased gassing.

The solid-electrolyte interphase (SEI) formed through the reductivedecomposition of solvent molecules plays a crucial role in theperformances of Si anode-based Li-ion batteries. It can help preventfurther electrolyte decomposition, thereby underlying capacityretention. The SEI also represents an electronically insulating barrierbetween the electrodes and electrolyte, with its composition, thickness,and structure influencing the lithium transport across the interphase.The performance enhancement achieved by the use of additives in the baseelectrolyte of Li-ion battery is therefore linked to the chemicalspecies formed in their decomposition which are incorporated into theSEI. On the cathode side, the additives should be oxidizedpreferentially to the solvent molecule in the bare electrolyte,resulting in a protective cathode electrolyte interphase (CEI) filmformed on the surface of the cathode. At the same time, the additive mayhelp alleviate the dissolution phenomenon of transition metal ions anddecrease surface resistance on the cathode side.

In the present disclosure, the use of nitrogen-containing compoundselectrode and/or electrolyte additives for energy storage devices isdescribed. Due to their unique chemical structures and functionalgroups, using nitrogen-containing compounds as electrolyte additives maybring the following benefits: (i) stabilize solid/electrolyte interfacefilm to reduce electrolyte reactions (oxidation on the NCM, NCA, or LCOcathode and reduction on the Si anode), prevent Si anode volumeexpansion, and protect transition metal ion dissolution from NCM or NCAcathode and stabilize the subsequent structure changes; and avoid theexothermic reaction between the released oxygen from cathodes and anorganic electrolyte and enhance the thermal stability of cathodes; and(ii) reduce the flammability and enhance the thermal stability oforganic electrolytes and increase the safety of electrolyte solutions.Due to their versatility in reaction chemistry and overall stability inelectrochemical environments, using nitrogen-containing compounds asadditives into electrolyte and/or electrode compositions may helpimprove both overall electrochemical performance and safety of Sianode-based Li-ion batteries. Nitrogen-containing compounds such asisocyanate may react to form more stable products, and the resultingproducts have a better affinity to the subsequently formed SEI and/ormay participate in SEI formation. In addition, the presence ofnitrogen-containing compounds as additives may assist in scavengingwater and acidic HF impurities from the electrolyte and/or aid inreducing undesired decomposition reactions.

When used as additives, nitrogen-containing compounds may be able toproduce a characteristic SEI with dense and low impedance, which caneffectively suppress the decomposition of electrolyte, HF generation,and LiF formation upon cycling. At the same time, the compounds may bemore stable on the positive electrode and they are not liable to beoxidatively decomposed when the battery works under severe conditionssuch as higher temperature or higher working voltage. The performance ofcells may depend on the nature of the nitrogen-containing compound (e.g.chemical structure) where factors such as stericsimilarities/differences, nature and position of potentialelectron-withdrawing groups, and the number and nature of heteroatomswithin the molecule can have a strong effect. In the present disclosure,the use of nitrogen-containing compounds as electrolyte and/or electrodeadditives for Si anode-based Li-ion batteries is described.

In the present disclosure, a simple process is described of usingnitrogen-containing chemicals as electrode additives by directly addingthem into an electrode slurry to prepare these additive-containingelectrodes for Li-ion batteries. The nitrogen-containing chemicals mayalso be used to modify separators to prepare different types offunctional separators for Li-ion batteries or Li-metal batteries.

Specifically considering the cathode, without negative impacts on theanode, electrolyte, and the battery manufacture procedures or design,adding cathode additives may be another efficient, cost-effective, andpractically feasible strategy to overcome the barriers of layeredcathode materials and to finally improve the full cell performance. Inthe present disclosure a simple process is described to prepare theseadditive-containing cathodes where nitrogen-based compounds may be addedinto a normal cathode-coating slurry; may be added by directly addingthem into an electrolyte solution containing the additives, or may beadded by dipping the prepared cathodes into their solutions; they canthus be loaded inside the cathodes or on the surface of the cathodes.These additives may help improve structural stability and enhance theionic conductivity of the cathode materials due to their weakerinteractions.

As discussed above, typical electrodes include a current collector suchas a copper sheet. Carbon is deposited onto the collector along with aninactive binder material. Carbon is often used because it has excellentelectrochemical properties and is also electrically conductive. If thecurrent collector layer (e.g., copper layer) was removed, the carbonwould likely be unable to mechanically support itself. Therefore,conventional electrodes require a support structure such as thecollector to be able to function as an electrode. The electrode (e.g.,anode or cathode) compositions described in this application can produceself-supported electrodes. The need for a metal foil current collectoris eliminated or minimized because the conductive carbonized polymer isused for current collection in the anode structure as well as formechanical support. In typical applications for the mobile industry, ametal current collector is typically added to ensure sufficient rateperformance. The carbonized polymer can form a substantially continuousconductive carbon phase in the entire electrode as opposed toparticulate carbon suspended in a non-conductive binder in one class ofconventional lithium-ion battery electrodes. Advantages of a carboncomposite blend that utilizes a carbonized polymer can include, forexample, 1) higher capacity, 2) enhanced overcharge/dischargeprotection, 3) lower irreversible capacity due to the elimination (orminimization) of metal foil current collectors, and 4) potential costsavings due to simpler manufacturing.

In order to increase the volumetric and gravimetric energy density oflithium-ion batteries, silicon may be used as the active material forthe cathode or anode. Several types of silicon materials, e.g., siliconnanopowders, silicon nanofibers, porous silicon, and ball-milledsilicon, have also been reported as viable candidates as activematerials for the negative or positive electrodes. Small particle sizes(for example, sizes in the nanometer range) generally can increase cyclelife performance. They also can display very high initial irreversiblecapacity. However, small particle sizes also can result in very lowvolumetric energy density (for example, for the overall cell stack) dueto the difficulty of packing the active material. Larger particle sizes,(for example, sizes in the micron range) generally can result in higherdensity anode material. However, the expansion of the silicon activematerial can result in poor cycle life due to particle cracking. Forexample, silicon can swell over 300% upon lithium insertion. Because ofthis expansion, anodes including silicon should be allowed to expandwhile maintaining electrical contact between the silicon particles.

Cathode electrodes (positive electrodes) described herein may includemetal oxide cathode materials, such as Lithium Cobalt Oxide (LiCoO₂)(LCO), Ni-rich oxides, high voltage cathode materials, lithium-richoxides, nickel-rich layered oxides, lithium-rich layered oxides,high-voltage spinel oxides, and high-voltage polyanionic compounds.Ni-rich oxides and/or high voltage cathode materials may include NCM andNCA. Example of NCM materials include, but are not limited to,LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ (NCM-622) and LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂(NCM-811). Lithium-rich oxides may includexLi₂Mn₃O₂.(1-x)LiNi_(a)Co_(b)Mn_(c)O₂. Nickel-rich layered oxides mayinclude LiNi_(1+x)M_(1−x)O_(z) (where M=Co, Mn or Al). Lithium-richlayered oxides may include LiNi_(1+x)M_(1−x)O₂ (where M=Co, Mn or Ni).High-voltage spinel oxides may include LiNi_(0.5)Mn_(1.5)O₄.High-voltage polyanionic compounds may include phosphates, sulfates,silicates, etc.

In certain embodiments, the positive electrode may be one of NCA, NCM,LMO or LCO. The NCM cathodes include NCM 9 0.5 0.5, NCM811, NCM622,NCM532, NCM433, NCM111, and others. In further embodiments, the positiveelectrode comprises a lithium-rich layered oxidexLi₂MnO₃.(1-x)LiNi_(a)Co_(b)Mn_(c)O₂; nickel-rich layered oxideLiNi_(1−x)M_(x)O₂ (M=Co, Mn and Al); or lithium rich layered oxideLiNi_(1+x)M_(1−x)O₂ (M=Co, Mn and Ni) cathode. In some embodiments,nitrogen-containing compounds may be used as electrolyte additives forSi-dominant anode//LiCoO₂ (LCO), LiNi_(x)Co_(y)Mn_(z)O₂ (NCM, 0≤x, y,z<1) or LiNi_(x)Co_(y)Al_(z)O₂ (NCA, 0≤x, y, z<1) cathode full cells.

As described herein and in U.S. patent application Ser. Nos. 13/008,800and 13/601,976, entitled “Composite Materials for ElectrochemicalStorage” and “Silicon Particles for Battery Electrodes,” respectively,certain embodiments utilize a method of creating monolithic,self-supported anodes using a carbonized polymer. Because the polymer isconverted into an electrically conductive and electrochemically activematrix, the resulting electrode is conductive enough that, in someembodiments, a metal foil or mesh current collector can be omitted orminimized. The converted polymer also acts as an expansion buffer forsilicon particles during cycling so that a high cycle life can beachieved. In certain embodiments, the resulting electrode is anelectrode that is comprised substantially of active material. In furtherembodiments, the resulting electrode is substantially active material.The electrodes can have a high energy density of between about 500 mAh/gto about 1200 mAh/g that can be due to, for example, 1) the use ofsilicon, 2) elimination or substantial reduction of metal currentcollectors, and 3) being comprised entirely or substantially entirely ofactive material.

As described herein and in U.S. patent application Ser. No. 14/800,380,entitled “Electrolyte Compositions for Batteries,” the entirety of whichis hereby incorporated by reference, composite materials can be used asan anode in most conventional Li-ion batteries; they may also be used asthe cathode in some electrochemical couples with additional additives.The composite materials can also be used in either secondary batteries(e.g., rechargeable) or primary batteries (e.g., non-rechargeable). Insome embodiments, the composite materials can be used in batteriesimplemented as a pouch cell, as described in further details herein. Incertain embodiments, the composite materials are self-supportedstructures. In further embodiments, the composite materials areself-supported monolithic structures. For example, a collector may beincluded in the electrode comprised of the composite material. Incertain embodiments, the composite material can be used to form carbonstructures discussed in U.S. patent application Ser. No. 12/838,368entitled “Carbon Electrode Structures for Batteries,” the entirety ofwhich is hereby incorporated by reference. Furthermore, the compositematerials described herein can be, for example, silicon compositematerials, carbon composite materials, and/or silicon-carbon compositematerials.

In some embodiments, the largest dimension of the silicon particles canbe less than about 40 μm, less than about 1 μm, between about 10 nm andabout 40 μm, between about 10 nm and about 1 μm, less than about 500 nm,less than about 100 nm, and about 100 nm. All, substantially all, or atleast some of the silicon particles may comprise the largest dimensiondescribed above. For example, an average or median largest dimension ofthe silicon particles can be less than about 40 μm, less than about 1μm, between about 10 nm and about 40 μm, between about 10 nm and about 1μm, less than about 500 nm, less than about 100 nm, and about 100 nm.The amount of silicon in the composite material can be greater than zeropercent by weight of the mixture and composite material. In certainembodiments, the mixture comprises an amount of silicon, the amountbeing within a range of from about 0% to about 95% by weight, includingfrom about 30% to about 95% by weight of the mixture. The amount ofsilicon in the composite material can be within a range of from about 0%to about 35% by weight, including from about 0% to about 25% by weight,from about 10% to about 35% by weight, and about 20% by weight. Infurther certain embodiments, the amount of silicon in the mixture is atleast about 30% by weight; greater than 0% and less than about 95% byweight; or between about 50% and about 95% by weight. Additionalembodiments of the amount of silicon in the composite material includemore than about 50% by weight, between about 30% and about 95% byweight, between about 50% and about 85% by weight, and between about 75%and about 95% by weight. Furthermore, the silicon particles may or maynot be pure silicon. For example, the silicon particles may besubstantially silicon or may be a silicon alloy. In one embodiment, thesilicon alloy includes silicon as the primary constituent along with oneor more other elements.

As described herein, micron-sized silicon particles can provide goodvolumetric and gravimetric energy density combined with good cycle life.In certain embodiments, to obtain the benefits of both micron-sizedsilicon particles (e.g., high energy density) and nanometer-sizedsilicon particles (e.g., good cycle behavior), silicon particles canhave an average particle size in the micron range and a surfaceincluding nanometer-sized features. In some embodiments, the siliconparticles have an average particle size (e.g., average diameter oraverage largest dimension) between about 0.1 μm and about 30 μm orbetween about 0.1 μm and all values up to about 30 μm. For example, thesilicon particles can have an average particle size between about 0.5 μmand about 25 μm, between about 0.5 μm and about 20 μm, between about 0.5μm and about 15 μm, between about 0.5 μm and about 10 μm, between about0.5 μm and about 5 μm, between about 0.5 μm and about 2 μm, betweenabout 1 μm and about 20 μm, between about 1 μm and about 15 μm, betweenabout 1 μm and about 10 μm, between about 5 μm and about 20 μm, etc.Thus, the average particle size can be any value between about 0.1 μmand about 30 μm, e.g., 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm,25 μm, and 30 μm.

The composite material can be formed by pyrolyzing a polymer precursor,such as polyamide acid. The amount of carbon obtained from the precursorcan be about 50 weight percent by weight of the composite material. Incertain embodiments, the amount of carbon from the precursor in thecomposite material is about 10% to about 25% by weight. The carbon fromthe precursor can be hard carbon. Hard carbon can be a carbon that doesnot convert into graphite even with heating over 2800 degrees Celsius.Precursors that melt or flow during pyrolysis convert into soft carbonsand/or graphite with sufficient temperature and/or pressure. Hard carbonmay be selected since soft carbon precursors may flow and soft carbonsand graphite are mechanically weaker than hard carbons. Other possiblehard carbon precursors can include phenolic resins, epoxy resins, andother polymers that have a very high melting point or are crosslinked. Asoft carbon precursor can be used if it does not melt at the heattreatment temperatures used. In some embodiments, the amount of carbonin the composite material has a value within a range of from about 10%to about 25% by weight, about 20% by weight, or more than about 50% byweight. In some embodiments, there may be greater than 0% and less thanabout 90% by weight of one or more types of carbon phases. In certainembodiments, the carbon phase is substantially amorphous. In otherembodiments, the carbon phase is substantially crystalline. In furtherembodiments, the carbon phase includes amorphous and crystalline carbon.The carbon phase can be a matrix phase in the composite material. Thecarbon can also be embedded in the pores of the additives includingsilicon. The carbon may react with some of the additives to create somematerials at interfaces. For example, there may be a silicon carbidelayer between the silicon particles and the carbon.

In certain embodiments, graphite particles are added to the mixture.Advantageously, graphite can be an electrochemically active material inthe battery as well as an elastically deformable material that canrespond to the volume change of the silicon particles. Graphite is thepreferred active anode material for certain classes of lithium-ionbatteries currently on the market because it has a low irreversiblecapacity. Additionally, graphite is softer than hard carbon and canbetter absorb the volume expansion of silicon additives. In certainembodiments, the largest dimension of the graphite particles is betweenabout 0.5 microns and about 20 microns. All, substantially all, or atleast some of the graphite particles may comprise the largest dimensiondescribed herein. In further embodiments, an average or median largestdimension of the graphite particles is between about 0.5 microns andabout 20 microns. In certain embodiments, the mixture includes greaterthan 0% and less than about 80% by weight of graphite particles. Infurther embodiments, the composite material includes about 1% to about20% by weight graphite particles. In further embodiments, the compositematerial includes about 40% to about 75% by weight graphite particles.

In certain embodiments, conductive particles which may also beelectrochemically active are added to the mixture. Such particles canenable both a more electronically conductive composite as well as a moremechanically deformable composite capable of absorbing the largevolumetric change incurred during lithiation and de-lithiation. Incertain embodiments, a largest dimension of the conductive particles isbetween about 10 nanometers and about 7 millimeters. All, substantiallyall, or at least some of the conductive particles may comprise thelargest dimension described herein. In further embodiments, an averageor median largest dimension of the conductive particles is between about10 nm and about 7 millimeters. In certain embodiments, the mixtureincludes greater than zero and up to about 80% by weight conductiveparticles. In further embodiments, the composite material includes about45% to about 80% by weight conductive particles. The conductiveparticles can be conductive carbon including carbon blacks, carbonfibers, carbon nanofibers, carbon nanotubes, graphite, graphene, etc.Many carbons that are considered as conductive additives that are notelectrochemically active become active once pyrolyzed in a polymermatrix. Alternatively, the conductive particles can be metals or alloysincluding copper, nickel, or stainless steel.

The composite material may also be formed into a powder. For example,the composite material can be ground into a powder. The compositematerial powder can be used as an active material for an electrode. Forexample, the composite material powder can be deposited on a collectorin a manner similar to making a conventional electrode structure, asknown in the industry.

In some embodiments, the full capacity of the composite material may notbe utilized during the use of the battery in order to improve batterylife (e.g., number charge and discharge cycles before the battery failsor the performance of the battery decreases below a usability level).For example, a composite material with about 70% by weight siliconparticles, about 20% by weight carbon from a precursor, and about 10% byweight graphite may have a maximum gravimetric capacity of about 2000mAh/g, while the composite material may only be used up to a gravimetriccapacity of about 550 to about 850 mAh/g. Although, the maximumgravimetric capacity of the composite material may not be utilized,using the composite material at a lower capacity can still achieve ahigher capacity than certain lithium-ion batteries. In certainembodiments, the composite material is used or only used at agravimetric capacity below about 70% of the composite material's maximumgravimetric capacity. For example, the composite material is not used ata gravimetric capacity above about 70% of the composite material'smaximum gravimetric capacity. In further embodiments, the compositematerial is used or only used at a gravimetric capacity below about 60%of the composite material's maximum gravimetric capacity or below about50% of the composite material's maximum gravimetric capacity.

An electrolyte composition for a lithium-ion battery can include asolvent and a lithium-ion source, such as a lithium-containing salt. Thecomposition of the electrolyte may be selected to provide a lithium-ionbattery with improved performance. In some embodiments, the electrolytemay contain an electrolyte additive. As described herein, a lithium-ionbattery may include a first electrode, a second electrode, a separatorbetween the first electrode and the second electrode, and an electrolytein contact with the first electrode, the second electrode, and theseparator. The electrolyte serves to facilitate ionic transport betweenthe first electrode and the second electrode. In some embodiments, thefirst electrode and the second electrode can refer to anode and cathodeor cathode and anode, respectively. Electrolytes and/or electrolytecompositions may be a liquid, solid, or gel.

In lithium-ion batteries, the most widely used electrolytes arenon-aqueous liquid electrolytes; these may comprise a lithium-containingsalt (e.g. LiPF₆) and low molecular weight carbonate solvents as well asvarious small amounts of functional additives. LiPF₆ holds a dominantposition in commercial liquid electrolytes due to its well-balancedproperties. However, LiPF₆ has problems such as high reactivity towardsmoisture and poor thermal stability. These issues are primarilyattributed to the equilibrium decomposition reaction of LiPF₆. The P—Fbond in LiPF₆ and PF₅ is rather labile towards hydrolysis by inevitabletrace amounts of moisture in batteries. Besides, as a strong Lewis acid,PF₅ is also able to initiate reactions with carbonate solvents andcauses further electrolyte degradation. Moreover, a temperature risefurther accelerates the decomposition reaction of LiPF₆ and consequentlypromotes subsequent parasitic reactions. This is also a reason forfaster aging of current lithium-ion batteries at elevated temperatures,as compared to room temperature.

In some embodiments, the electrolyte for a lithium ion battery mayinclude a solvent comprising a fluorine-containing component, such as afluorine-containing cyclic carbonate, a fluorine-containing linearcarbonate, and/or a fluoroether. In some embodiments, the electrolytecan include more than one solvent. For example, the electrolyte mayinclude two or more co-solvents. In some embodiments, at least one ofthe co-solvents in the electrolyte is a fluorine-containing compound. Insome embodiments, the fluorine-containing compound may be fluoroethylenecarbonate (FEC), or difluoroethylene carbonate (F2EC). In someembodiments, the co-solvent may be selected from the group consisting ofFEC, ethyl methyl carbonate (EMC), 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, difluoroethylene carbonate (F2EC),ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate(DMC), propylene carbonate (PC), Dimethoxy ethane (DME), andgamma-butyrolactone (GBL), methyl acetate (MA), ethyl acetate (EA), andmethyl propanoate. In some embodiments, the electrolyte contains FEC. Insome embodiments, the electrolyte contains both EMC and FEC. In someembodiments, the electrolyte may further contain1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, EC, DEC, DMC,PC, GBL, and/or F2EC or some partially or fully fluorinated linear orcyclic carbonates, ethers, etc. as a co-solvent. In some embodiments,the electrolyte is free or substantially free of non-fluorine-containingcyclic carbonates, such as EC, GBL, and PC.

In further embodiments, electrolyte solvents may be composed of a cycliccarbonate, such as fluoro ethylene carbonate (FEC), di-fluoroethylenecarbonate (DiFEC), Trifluoropropylene carbonate (TFPC), ethylenecarbonate (EC), propylene carbonate (PC), etc; a linear carbonate, suchas dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methylcarbonate (EMC), etc, or other solvents, such as methyl acetate, ethylacetate, or gamma butyrolactone, dimethoxyethane,1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, etc.

In some embodiments, the electrolyte composition may comprise a systemof solvents (i.e. a solvent, plus one or more co-solvents). The solventsmay be fluorinated or non-fluorinated. In some embodiments, theco-solvents may be one or more linear carbonates, lactones, acetates,propanoates and/or non-linear carbonates. In some embodiments, theco-solvents may be one or more carbonate solvents, such as one or morelinear carbonates and/or non-linear carbonates, as discussed above. Insome embodiments, an electrolyte composition may comprise one or more ofEC at a concentration of 5% or more; FEC at a concentration of 5% ormore; and/or TFPC at a concentration of 5% or more.

In some embodiments, the solvents in the electrolyte compositioninclude, but are not limited to, one or more of ethyl methyl carbonate(EMC), methyl acetate, dimethyl carbonate (DMC), diethyl carbonate(DEC), gamma butyrolactone, methyl acetate (MA), ethyl acetate (EA),methyl propanoate, fluoro ethylene carbonate (FEC), di-fluoroethylenecarbonate (DiFEC), Trifluoropropylene carbonate (TFPC), ethylenecarbonate (EC), vinylene carbonate (VC) or propylene carbonate (PC). Infurther embodiments, the solvents include at least one of one or more ofethyl methyl carbonate (EMC), methyl acetate, dimethyl carbonate (DMC),diethyl carbonate (DEC), gamma butyrolactone, methyl acetate (MA), ethylacetate (EA), methyl propanoate, along with at least one or more offluoro ethylene carbonate (FEC), di-fluoroethylene carbonate (DiFEC),Trifluoropropylene carbonate (TFPC), ethylene carbonate (EC), vinylenecarbonate (VC) or propylene carbonate (PC).

As used herein, a co-solvent of an electrolyte has a concentration of atleast about 10% by volume (vol %). In some embodiments, a co-solvent ofthe electrolyte may be about 20 vol %, about 40 vol %, about 60 vol %,or about 80 vol %, or about 90 vol % of the electrolyte. In someembodiments, a co-solvent may have a concentration from about 10 vol %to about 90 vol %, from about 10 vol % to about 80 vol %, from about 10vol % to about 60 vol %, from about 20 vol % to about 60 vol %, fromabout 20 vol % to about 50 vol %, from about 30 vol % to about 60 vol %,or from about 30 vol % to about 50 vol %.

For example, in some embodiments, the electrolyte may contain afluorine-containing cyclic carbonate, such as FEC, at a concentration ofabout 10 vol % to about 60 vol %, including from about 20 vol % to about50 vol %, and from about 20 vol % to about 40 vol %. In someembodiments, the electrolyte may comprise a linear carbonate that doesnot contain fluorine, such as EMC, at a concentration of about 40 vol %to about 90 vol %, including from about 50 vol % to about 80 vol %, andfrom about 60 vol % to about 80 vol %. In some embodiments, theelectrolyte may comprise 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether at a concentration of from about 10 vol% to about 30 vol %, including from about 10 vol % to about 20 vol %.

In some embodiments, the electrolyte is substantially free of cycliccarbonates other than fluorine-containing cyclic carbonates (i.e.,non-fluorine-containing cyclic carbonates). Examples ofnon-fluorine-containing carbonates include EC, PC, GBL, and vinylenecarbonate (VC).

In some embodiments, the electrolyte may further comprise one or moreadditives. As used herein, an additive of the electrolyte refers to acomponent that makes up less than 10% by weight (wt %) of theelectrolyte. In some embodiments, the amount of each additive in theelectrolyte may be from about 0.2 wt % to about 1 wt %, 0.1 wt % toabout 2 wt %, 0.2 wt % to about 9 wt %, from about 0.5 wt % to about 9wt %, from about 1 wt % to about 9 wt %, from about 1 wt % to about 8 wt%, from about 1 wt % to about 8 wt %, from about 1 wt % to about 7 wt %,from about 1 wt % to about 6 wt %, from about 1 wt % to about 5 wt %,from about 2 wt % to about 5 wt %, or any value in between. In someembodiments, the total amount of the additive(s) may be from about 1 wt% to about 9 wt %, from about 1 wt % to about 8 wt %, from about 1 wt %to about 7 wt %, from about 2 wt % to about 7 wt %, or any value inbetween. In other embodiments, the percentages of additives may beexpressed in volume percent (vol %).

The electrolyte additive may comprise nitrogen-containing compounds, asdescribed herein. In some embodiments, the electrolyte composition maycontain the compound as an additive at less than 10 weight %; or at lessthan 5 weight %. In other embodiments, the electrolyte composition maycontain the compound as an additive at less than 1 wt % or less; inother embodiments, about 0.5 wt % or less or about 0.2 wt % or less isutilized.

The term “alkyl” refers to a straight or branched, saturated, aliphaticradical having the number of carbon atoms indicated. The alkyl moietymay be branched or straight chain. For example, C1-C6 alkyl includes,but is not limited to, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, etc. Otheralkyl groups include, but are not limited to heptyl, octyl, nonyl,decyl, etc. Alkyl can include any number of carbons, such as 1-2, 1-3,1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12 2-3, 2-4, 2-5, 2-6, 3-4,3-5, 3-6, 4-5, 4-6 and 5-6. The alkyl group is typically monovalent, butcan be divalent, such as when the alkyl group links two moietiestogether.

The term “fluoro-alkyl” refers to an alkyl group where one, some, or allhydrogen atoms have been replaced by fluorine.

The term “alkylene” refers to an alkyl group, as defined above, linkingat least two other groups, i.e., a divalent hydrocarbon radical. The twomoieties linked to the alkylene can be linked to the same atom ordifferent atoms of the alkylene. For instance, a straight chain alkylenecan be the bivalent radical of —(CH₂)_(n)—, where n is 1, 2, 3, 4, 5, 6,7, 8, 9, or 10. Alkylene groups include, but are not limited to,methylene, ethylene, propylene, isopropylene, butylene, isobutylene,sec-butylene, pentylene and hexylene.

The term “alkoxy” refers to alkyl group having an oxygen atom thateither connects the alkoxy group to the point of attachment or is linkedto two carbons of the alkoxy group. Alkoxy groups include, for example,methoxy, ethoxy, propoxy, iso-propoxy, butoxy, 2-butoxy, iso-butoxy,sec-butoxy, tert-butoxy, pentoxy, hexoxy, etc. The alkoxy groups can befurther substituted with a variety of substituents described within. Forexample, the alkoxy groups can be substituted with halogens to form a“halo-alkoxy” group, or substituted with fluorine to form a“fluoro-alkoxy” group.

The term “alkenyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one double bond.Examples of alkenyl groups include, but are not limited to, vinyl,propenyl, isopropenyl, 1-butenyl, 2-butenyl, isobutenyl, butadienyl,1-pentenyl, 2-pentenyl, isopentenyl, 1,3-pentadienyl, 1,4-pentadienyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 1,3-hexadienyl, 1,4-hexadienyl,1,5-hexadienyl, 2,4-hexadienyl, or 1,3,5-hexatrienyl. Alkenyl groups canalso have from 2 to 3, 2 to 4, 2 to 5, 3 to 4, 3 to 5, 3 to 6, 4 to 5, 4to 6 and 5 to 6 carbons. The alkenyl group is typically monovalent, butcan be divalent, such as when the alkenyl group links two moietiestogether.

The term “alkenylene” refers to an alkenyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkenylene can be linked to the same atomor different atoms of the alkenylene. Alkenylene groups include, but arenot limited to, ethenylene, propenylene, isopropenylene, butenylene,isobutenylene, sec-butenylene, pentenylene and hexenylene.

The term “alkynyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one triple bond.Examples of alkynyl groups include, but are not limited to, acetylenyl,propynyl, 1-butynyl, 2-butynyl, isobutynyl, sec-butynyl, butadiynyl,1-pentynyl, 2-pentynyl, isopentynyl, 1,3-pentadiynyl, 1,4-pentadiynyl,1-hexynyl, 2-hexynyl, 3-hexynyl, 1,3-hexadiynyl, 1,4-hexadiynyl,1,5-hexadiynyl, 2,4-hexadiynyl, or 1,3,5-hexatriynyl. Alkynyl groups canalso have from 2 to 3, 2 to 4, 2 to 5, 3 to 4, 3 to 5, 3 to 6, 4 to 5, 4to 6 and 5 to 6 carbons. The alkynyl group is typically monovalent, butcan be divalent, such as when the alkynyl group links two moietiestogether.

The term “alkynylene” refers to an alkynyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkynylene can be linked to the same atomor different atoms of the alkynylene. Alkynylene groups include, but arenot limited to, ethynylene, propynylene, butynylene, sec-butynylene,pentynylene, and hexynylene.

The term “cycloalkyl” refers to a saturated or partially unsaturated,monocyclic, fused bicyclic, bridged polycyclic, or spiro ring assemblycontaining from 3 to 12, from 3 to 10, or from 3 to 7 ring atoms, or thenumber of atoms indicated. Monocyclic rings include, for example,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl.Bicyclic and polycyclic rings include, for example, norbornane,decahydronaphthalene and adamantane. For example, C3-C8 cycloalkylincludes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl,and norbornane. As used herein, the term “fused” refers to two ringswhich have two atoms and one bond in common. For example, in thefollowing structure, rings A and B are fused

As used herein, the term “bridged polycyclic” refers to compoundswherein the cycloalkyl contains a linkage of one or more atomsconnecting non-adjacent atoms. The following structures

are examples of “bridged” rings. As used herein, the term “spiro” refersto two rings that have one atom in common and the two rings are notlinked by a bridge. Examples of fused cycloalkyl groups aredecahydronaphthalenyl, dodecahydro-1H-phenalenyl andtetradecahydroanthracenyl; examples of bridged cycloalkyl groups arebicyclo[1.1.1]pentyl, adamantanyl, and norbornanyl; and examples ofspiro cycloalkyl groups include spiro[3.3]heptane and spiro[4.5]decane.

The term “cycloalkylene” refers to a cycloalkyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the cycloalkylene can be linked to the sameatom or different atoms of the cycloalkylene. Cycloalkylene groupsinclude, but are not limited to, cyclopropylene, cyclobutylene,cyclopentylene, cyclohexylene, and cyclooctylene.

The term “aryl” refers to a monocyclic or fused bicyclic, tricyclic orgreater, aromatic ring assembly containing 6 to 16 ring carbon atoms.For example, aryl may be phenyl, benzyl or naphthyl, preferably phenyl.Aryl groups may include fused multicyclic ring assemblies wherein onlyone ring in the multicyclic ring assembly is aromatic. Aryl groups canbe mono-, di-, or tri-substituted by one, two or three radicals.Preferred as aryl is naphthyl, phenyl, or phenyl mono- or disubstitutedby alkoxy, phenyl, halogen, alkyl or trifluoromethyl, especially phenylor phenyl-mono- or disubstituted by alkoxy, halogen or trifluoromethyl,and in particular phenyl.

The term “arylene” refers to an aryl group, as defined above, linking atleast two other groups. The two moieties linked to the arylene arelinked to different atoms of the arylene. Arylene groups include, butare not limited to, phenylene.

The term “heteroaryl” refers to a monocyclic or fused bicyclic ortricyclic aromatic ring assembly containing 5 to 16 ring atoms, wherefrom 1 to 4 of the ring atoms are a heteroatom such as N, O, or S. Forexample, heteroaryl includes pyridyl, indolyl, indazolyl, quinoxalinyl,quinolinyl, isoquinolinyl, benzothienyl, benzofuranyl, furanyl,pyrrolyl, thiazolyl, benzothiazolyl, oxazolyl, isoxazolyl, triazolyl,tetrazolyl, pyrazolyl, imidazolyl, thienyl, or any other radicalssubstituted, especially mono- or di-substituted, by e.g. alkyl, nitro orhalogen. Pyridyl represents 2-, 3- or 4-pyridyl, advantageously 2- or3-pyridyl. Thienyl represents 2- or 3-thienyl. Quinolinyl representspreferably 2-, 3- or 4-quinolinyl. Isoquinolinyl represents preferably1-, 3- or 4-isoquinolinyl. Benzopyranyl, benzothiopyranyl representspreferably 3-benzopyranyl or 3-benzothiopyranyl, respectively. Thiazolylrepresents preferably 2- or 4-thiazolyl, and most preferred 4-thiazolyl.Triazolyl is preferably 1-, 2- or 5-(1,2,4-triazolyl). Tetrazolyl ispreferably 5-tetrazolyl.

Preferably, heteroaryl is pyridyl, indolyl, quinolinyl, pyrrolyl,thiazolyl, isoxazolyl, triazolyl, tetrazolyl, pyrazolyl, imidazolyl,thienyl, furanyl, benzothiazolyl, benzofuranyl, isoquinolinyl,benzothienyl, oxazolyl, indazolyl, or any of the radicals substituted,especially mono- or di-substituted.

The term “heteroalkyl” refers to an alkyl group having from 1 to 3heteroatoms such as N, O and S. The heteroatoms can also be oxidized,such as, but not limited to, —S(O)— and —S(O)₂—. For example,heteroalkyl can include ethers, thioethers, alkyl-amines andalkyl-thiols.

The term “heteroalkylene” refers to a heteroalkyl group, as definedabove, linking at least two other groups. The two moieties linked to theheteroalkylene can be linked to the same atom or different atoms of theheteroalkylene.

The term “heterocycloalkyl” refers to a ring system having from 3 ringmembers to about 20 ring members and from 1 to about 5 heteroatoms suchas N, O and S. The heteroatoms can also be oxidized, such as, but notlimited to, —S(O)— and —S(O)₂—. For example, heterocycle includes, butis not limited to, tetrahydrofuranyl, tetrahydrothiophenyl, morpholino,pyrrolidinyl, pyrrolinyl, imidazolidinyl, imidazolinyl, pyrazolidinyl,pyrazolinyl, piperazinyl, piperidinyl, indolinyl, quinuclidinyl and1,4-dioxa-8-aza-spiro[4.5]dec-8-yl.

The term “heterocycloalkylene” refers to a heterocyclalkyl group, asdefined above, linking at least two other groups. The two moietieslinked to the heterocycloalkylene can be linked to the same atom ordifferent atoms of the heterocycloalkylene.

The term “optionally substituted” is used herein to indicate a moietythat can be unsubstituted or substituted by one or more substituent.When a moiety term is used without specifically indicating assubstituted, the moiety is unsubstituted.

In accordance with the disclosure, various functionalnitrogen-containing compounds may be used as one or more of electrolyteadditives, electrode additives (cathode or anode) and/or as separatormodifiers.

Examples of nitrogen-containing compounds include, but are not limitedto, compounds containing the following moieties: cyanate (—O—C≡N),thiocyanate (—S—C≡N), isothiocyanate (—N═C═S), isocyano (—N+≡C—),nitrile (—C≡N) groups, or other nitrogen-containing functional moieties.The nitrogen-containing compounds may also contain other functionalgroups such as alkenyl; heteroalkenyl; alkynyl; heteroalkynyl; alkyloptionally substituted by —F, —CN, —CF₃ or heterocycloalkyl; cycloalkyl;heterocycloalkyl; or combinations thereof. The nitrogen-containingcompounds may also contain other heterogeneous atoms in the structure,such as sulfur, oxygen, Si, P, or others.

In some embodiments, the nitrogen-containing compound as described abovemay be a compound with one or more functional substituents (groups,moieties) in addition to the nitrogen-containing moiety. Thenitrogen-containing compounds described herein may be furthersubstituted with substituents selected from the group consisting of H,OH, F, alkyl, fluoro-alkyl, alkylene, alkoxy, alkenyl, alkenylene,alkynyl, alkynylene, cycloalkyl, cycloalkylene, aryl, arylene,heteroaryl, heteroalkyl, heteroalkylene, heterocycloalkyl, andheterocycloalkylene, as defined above, which may be also furtheroptionally substituted, such as alkyl optionally substituted by F, CN,CF₃; or a combination thereof. The compound may also contain otherheterogeneous atoms in the structure, such as sulfur, oxygen, Si, P, orothers.

Substituents may be one or more alkenyl, alkenylene, alkynyl,alkynylene, cycloalkyl, cycloalkylene, aryl, arylene or heteroarylsubstituents, which are substituted by H, alkyl, fluoro-alkyl, alkylene,alkoxy, alkenyl, alkenylene, alkynyl, alkynylene, cycloalkyl,cycloalkylene, aryl, arylene, heteroaryl, heteroalkyl, heteroalkylene,heterocycloalkyl, and heterocycloalkylene, as described above, and whichmay be also further optionally substituted.

In some embodiments, the additives may be nitrogen-containing compoundswith different functional groups. The functional groups can be —NH,—NH₂, alkenyl, heteroalkenyl, alkynyl, heteroalkynyl, alkyl optionallysubstituted by —F, —CF₃ or heterocycloalkyl, a cycloalkyl, aheterocycloalkyl, etc. Some of these modifications may also include theuse of alkyl substituents, aromatic sub-cyclic units, nitrogen, silicon,and/or sulfur atoms substituted for oxygen in the macrocyclic ring andother changes or combinations thereof.

In some embodiments, the nitrogen-containing compound contains one ormore cyanate (—O—C≡N), thiocyanate (—S—C≡N), isothiocyanate (—N═C═S),isocyano (—N+≡C—), and/or nitrile (—C≡N) groups. In other embodiments,the nitrogen-containing compound is another nitrogen-containingfunctional chemical such as nitrogen-containing cyclic compounds, e.g.compounds containing piperidinyl moieties or azoles such asbenzotriazole; or nitrogen-containing compounds that also includesilicon.

In some embodiments, the nitrogen-containing compound is anisothiocyanate (—N═C═S) compound, which include but are not limited to1,4-Phenylene Diisothiocyanate (PDIST); Perfluorophenyl isothiocyanate(PFPIT); Benzyl isothiocyanate; Phenyl isothiocyanate;1-isothiocyanato-4-(trifluoromethoxy)benzene;3-fluoro-4-(MethylsulfonylaMino)benzyl isothiocyanate; ThienylmethylIsothiocyanate; 4-Cyanophenyl isothiocyanate; 4-Fluorophenylisothiocyanate; 2,4-Difluorophenyl isothiocyanate; 4-Nitrophenylisothiocyanate; 4-(Trifluoromethylthio)phenyl isocyanate; 3-Butenylisothiocyanate; 2,6-Diisopropylphenyl isothiocyanate; p-Vinylphenylisothiocyanate; allyl isothiocyanate; 3,5-Bis(trifluoromethyl)phenylisothiocyanate; Cyclohexyl Isothiocyanate; etc.

Example structures of nitrogen-containing compounds are shown below:

1,4-Phenylene Diisothiocyanate (PDIST)

Perfluorophenyl isothiocyanate (PFPIT)

benzyl isothiocyanate

Phenyl isothiocyanate

1-isothiocyanato-4-(trifluoromethoxy)benzene

3-fluoro-4-(MethylsulfonylaMino)benzyl isothiocyanate

Thienylmethyl Isothiocyanate

4-Cyanophenyl isothiocyanate

4-Fluorophenyl isothiocyanate

2,4-Difluorophenyl isothiocyanate

4-Nitrophenyl isothiocyanate

4-(Trifluoromethylthio)phenyl isocyanate

3-Butenyl isothiocyanate

2,6-Diisopropylphenyl isothiocyanate

p-Vinylphenyl isothiocyanate

allyl isothiocyanate

3,5-Bis(trifluoromethyl)phenyl isothiocyanate

Cyclohexyl Isothiocyanate

In some embodiments, the nitrogen-containing compound is a cyanate(—O—C≡N) compound, which include but are not limited to Methyl cyanate;(dicyanatoamino) cyanate; Phenyl Cyanate; Bisphenol A cyanate ester;etc.

Example structures of nitrogen-containing compounds are shown below:

Methyl cyanate

(dicyanatoamino) cyanate

Phenyl Cyanate

Bisphenol A cyanate ester

In some embodiments, the nitrogen-containing compound is a thiocyanate(—S—C≡N) compound, which include but are not limited to Ethylthiocyanate; Phenyl thiocyanate; 4-Phenoxy-phenoxyethyl thiocyanate;Isopropyl Thiocyanate; Allyl thiocyanate; 2-oxo-2-phenylethylthiocyanate; 4-amino phenyl thiocyanate; 2-furylmethyl thiocyanate; etc.

Example structures of nitrogen-containing compounds are shown below:

Ethyl thiocyanate

Phenyl thiocyanate

4-Phenoxy-phenoxyethyl thiocyanate

Isopropyl Thiocyanate

Allyl thiocyanate

2-oxo-2-phenylethyl thiocyanate

4-amino phenyl thiocyanate

2-furylmethyl thiocyanate

In some embodiments, the nitrogen-containing compound is an isocyano(—N+≡C—) compound, which include but are not limited to2-Isocyano-1,1-dimethoxyethane; 1-Isocyano-2,4-dimethylbenzene;Isocyanomethylbenzene; 1-Isocyano-3,5-dimethylbenzene;1-Isocyano-4-(trifluoromethoxy)benzene; 1-Fluoro-4-isocyanobenzene;4-isocyanobenzonitrile; 1,4-Phenylene diisocyanide; etc.

Example structures of nitrogen-containing compounds are shown below:

2-Isocyano-1,1-dimethoxyethane

1-Isocyano-2,4-dimethylbenzene

Isocyanomethylbenzene

Isocyano-3,5-dimethylbenzene

1-Isocyano-4-(trifluoromethoxy)benzene

1-Fluoro-4-isocyanobenzene

4-isocyanobenzonitrile

1,4-Phenylene diisocyanide

In some embodiments, the nitrogen-containing compound is a nitrile (—C≡N) compound, which include but are not limited to3-Thiophenecarbonitrile; Benzonitrile; 3-(Phenylsulfonyl)propionitrile;(Phenylsulfonyl)acetonitrile;[4-(Trifluoromethyl)phenylsulfonyl]acetonitrile; CN-alkyne; etc.

Example structures of nitrogen-containing compounds are shown below:

3-Thiophenecarbonitrile

Benzonitrile

3-(Phenylsulfonyl)propionitrile

(Phenylsulfonyl)acetonitrile

[4-(Trifluoromethyl)phenylsulfonyl]acetonitrile

CN-alkyne

In some embodiments, the nitrogen-containing compound is anothernitrogen-containing functional chemical such as nitrogen-containingcyclic compounds, which include but are not limited to2-(2′-Hydroxy-5′-methylphenyl)benzotriazole;2-(2′-Hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole;2-(2′-Hydroxy-5′-tert-octylphenyl)benzotriazole;2,2′-Methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol];6-(2-benzotriazolyl)-4-tert-octyl-6′-tert-butyl-4′-methyl-2,2′-methylenebisphenol;Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate;Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate; etc.; or anitrogen-containing compound that also includes silicon, such as3-(Triethoxysilyl)propyl isocyanate.

Example structures of nitrogen-containing compounds are shown below:

2-(2′-Hydroxy-5′-methylphenyl)benzotriazole

2-(2′-Hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole

2-(2′-Hydroxy-5′-tert-octylphenyl)benzotriazole

2,2′-Methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol]

6-(2-benzotriazolyl)-4-tert-octyl-6-tert-butyl-4′-methyl-2,2′-methylenebisphenol

Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate

Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate

3-(Triethoxysilyl)propyl isocyanate (Si-isocy)

In further embodiments, the nitrogen-containing compound may be used tocreate a treated power, e.g. an isocyanate-treated Si powder, which maybe used to a prepare Si-dominant anodes. In additional embodiments, thenitrogen-containing functional chemicals, as disclosed above, may beused as cathode additives by directly adding them into different typesof cathode slurries.

Nitrogen-containing functional compounds are believed to undergoelectrochemical reductive polymerization at higher potential and therebyprevent further electrolyte degradation on the surface of anodes. Ifreduction is initiated by the reaction of the functional group of acompound such as isocyanate, an isocyanate monomer may be converted intoan intermediate. The formed intermediate may then react either withanother isocyanate monomer resulting in a polymeric material which couldthen participate in the building up of the SEI and/or could react withother electrolyte components (e.g. solvents or salts), leading to amixed reduction and SEI-building products. These nitrogen-containingcompounds may also build an efficient passivation layer to alleviate theside reaction between the electrolyte and cathode at high potential,thus forming stable CEI layer. Besides serving as SEI or CEI precursors,the nitrogen-containing compounds can also scavenge H₂O and HFimpurities from the electrolyte solution, thus minimizing theirdeleterious effect in the battery systems.

The use of functional compound additives is a viable, economical andcost-effective strategy to modify the surface chemistry in batteries.This allows for potential circumvention of the massive volume change andinitial capacity loss due to the continuous electrolyte decomposition inhigh capacity and reactive electrodes, such as Si anodes, Ni-rich NCA orNCM cathodes. Compound additives can be directly added into the cathodeslurries, anode (e.g. Si) slurries or used as electrolyte additives.Additives can modify the SEI or CEI interphases in Li-ion batteries,thus altering and tuning their composition and correspondingelectrochemical properties, such as cycle life, rate capability,energy/power densities, etc. In one embodiment, the functional compoundadditives are utilized as cathode additives to improve cycle performanceof Li[Ni_(x)Co_(y)Al_(1−x−y)]O₂ (NCA) or Li[Ni_(x)Co_(y)Mn_(1−x−y)]O₂(NCM) cathode-based Li-ion full cells with Si-dominant anodes.

Compound additives, as part of electrode compositions, can form a SEIlayer that can reduce or prevent the cracking and/or the continuousreduction of electrolyte solutions as the silicon-containing anodeexpands and contracts during cycling. Furthermore, these electrolyteadditives, along with the electrolyte solvents in the electrolytecomposition, may be oxidized on a cathode surface to form a CEI layerthat can suppress or minimize further decomposition of the electrolyteon the surface of the cathode. Without being bound to the theory or modeof operation, it is believed that the presence of nitrogen-containingcompounds can result in a SEI and/or CEI layer on the surface ofelectrodes with improved performance. An SEI layer comprisingnitrogen-containing compounds may demonstrate improved chemicalstability and increased density, for example, compared to SEI layersformed by electrolytes without additives or with traditional additives.As such, the change in thickness and surface reactivity of the interfacelayer is limited, which may, in turn, facilitate reduction in capacityfade and/or generation of excessive gaseous byproducts during operationof the lithium-ion battery. A CEI layer comprising nitrogen-containingcompounds may help minimize transition metal ion dissolution andstructure changes on the cathode side and may provide favorable kineticsresulting in improved cycling stability and rate capability.

An electrolyte composition for a lithium-ion battery can include one ormore solvents, a lithium-ion source, such as a lithium-containing salt,and one or more electrolyte additives. As discussed above, incorporatingnitrogen-containing compounds as electrolyte additives into electrolytecompositions may help improve both overall electrochemical performanceand safety of Si anode-based Li-ion batteries. In some embodiments, theelectrolyte additives may be one or more of the disclosednitrogen-containing compounds.

As discussed above, a lithium-ion battery typically includes a separatorand/or electrolyte between an anode and a cathode. Separators may beformed as sheets or films, which are then stacked or rolled with theanode and cathode (e.g., electrodes) to form the battery. The separatormay comprise a single continuous or substantially continuous sheet orfilm, which can be interleaved between adjacent electrodes of theelectrode stack. The separator may be configured to facilitateelectrical insulation between the anode and the cathode, while stillpermitting ionic transport. In some embodiments, the separator maycomprise a porous material. In some embodiments, functionalnitrogen-containing compounds are used to modify the separator toprepare different types of functional separators to improve the cycleperformance of Li-ion batteries or Li-metal batteries.

In some embodiments, salts may be included in the electrolytecompositions. A lithium-containing salt for a lithium-ion battery maycomprise a fluorinated or non-fluorinated salt. In further embodiments,a lithium-containing salt for a lithium-ion battery may comprise one ormore of lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate(LiBF₄), lithium hexafluoroarsenate monohydrate (LiAsF₆), lithiumperchlorate (LiClO₄), lithium bis(trifluoromethanesulfonyl)imide(LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithiumbis(oxalato)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB),lithium triflate (LiCF₃SO₃), lithium tetrafluorooxalato phosphate(LTFOP), lithium difluorophosphate (LiPO₂F₂), lithiumpentafluoroethyltrifluoroborate (LiFAB), and lithium2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), lithiumbis(2-fluoromalonato)borate (LiBFMB), lithium 4-pyridyl trimethyl borate(LPTB), lithium 2-fluorophenol trimethyl borate (LFPTB), lithiumcatechol dimethyl borate (LiCDMB), lithium tetrafluorooxalatophosphate(LiFOP), etc. or combinations thereof. In certain embodiments, alithium-containing salt for a lithium-ion battery may comprise lithiumhexafluorophosphate (LiPF₆). In some embodiments, the electrolyte canhave a salt concentration of about 1 moles/L (M). In other embodiments,the salt concentration can be higher than 1 M; in further embodiments,the salt concentration can be higher than 1.2M.

In some embodiments, a lithium-ion battery comprising an electrolytecomposition according to one or more embodiments described herein, andan anode having a composite electrode film according to one or moreembodiments described herein, may demonstrate reduced gassing and/orswelling at about room temperature (e.g., about 20° C. to about 25° C.)or elevated temperatures (e.g., up to temperatures of about 85° C.),increased cycle life at about room temperature or elevated temperatures,and/or reduced cell growth/electrolyte consumption per cycle, forexample, compared to lithium-ion batteries comprising conventionallyavailable electrolyte compositions in combination with an anode having acomposite electrode film according to one or more embodiments describedherein. In some embodiments, a lithium-ion battery comprising anelectrolyte composition according to one or more embodiments describedherein and an anode having a composite electrode film according to oneor more embodiments described herein may demonstrate reduced gassingand/or swelling across various temperatures at which the battery may besubject to testing, such as temperatures between about −20° C. and about130° C. (e.g., compared to lithium-ion batteries comprisingconventionally available electrolyte compositions in combination with ananode having a composite electrode film according to one or moreembodiments described herein).

Gaseous by-products may be undesirably generated during batteryoperation, for example, due to chemical reactions between theelectrolyte and one or more other components of the lithium-ion battery,such as one or more components of a battery electrode. Excessive gasgeneration during the operation of the lithium-ion battery may adverselyaffect battery performance and/or result in mechanical and/or electricalfailure of the battery. For example, undesired chemical reactionsbetween an electrolyte and one or more components of an anode may resultin gas generation at levels that can mechanically (e.g., structuraldeformation) and/or electrochemically degrade the battery. In someembodiments, the composition of the anode and the composition of theelectrolyte can be selected to facilitate desired gas generation.

The electrolytes and electrolyte additives described herein may beadvantageously utilized within an energy storage device. In someembodiments, energy storage devices may include batteries, capacitors,and battery-capacitor hybrids. In some embodiments, the energy storagedevice comprises lithium. In some embodiments, the energy storage devicemay comprise at least one electrode, such as an anode and/or cathode. Insome embodiments, at least one electrode may be a Si-based electrode. Insome embodiments, the Si-based electrode is a Si-dominant electrode,where silicon is the majority of the active material used in theelectrode (e.g., greater than 50% silicon). In some embodiments, theenergy storage device comprises a separator. In some embodiments, theseparator is between a first electrode and a second electrode.

In some embodiments, the amount of silicon in the electrode material(active material) includes between about 30% and about 95% by weight,between about 50% and about 85% by weight, and between about 75% andabout 95% by weight. In other embodiments, the amount of silicon in theelectrode material may be at least about 30% by weight; greater than 0%and less than about 95% by weight; or between about 50% and about 95% byweight. Furthermore, the silicon particles may or may not be puresilicon. For example, the silicon particles may be substantially siliconor may be a silicon alloy. In one embodiment, the silicon alloy includessilicon as the primary constituent along with one or more otherelements.

In some embodiments, the energy storage device comprises an electrolytecomposition. In some embodiments, the electrolyte composition comprisesone or more of a salt, solvent, solvent additive/co-solvent, and/oradditive compound as described herein. For example, in some embodiments,the electrolyte comprises one or more additive nitrogen-containingcompounds as described herein.

FIG. 2A is a flow diagram of a lamination process for forming asilicon-dominant anode cell, in accordance with an example embodiment ofthe disclosure. This process employs a high-temperature pyrolysisprocess on a substrate, layer removal, and a lamination process toadhere the active material layer to a current collector. This strategymay also be adopted by other anode-based cells, such as graphite,conversion type anodes, such as transition metal oxides, transitionmetal phosphides, and other alloy type anodes, such as Sn, Sb, Al, P,etc.

The raw electrode active material is mixed in step 201. In the mixingprocess, the active material may be mixed with a binder/resin (such aswater-soluble PI, PAI, Phenolic or other water-soluble resins andmixtures and combinations thereof), solvent, rheology modifiers,surfactants, pH modifiers, and conductive additives. The materials maycomprise carbon nanotubes/fibers, graphene sheets, metal polymers,metals, semiconductors, and/or metal oxides, for example. In oneembodiment, silicon powder with a 1-30 or 5-30 μm particle size, forexample, may then be dispersed in polyamic acid resin, polyamideimide,or polyimide (15-25% solids in N-Methyl pyrrolidone (NMP) or DI water)at, e.g., 1000 rpm for, e.g., 10 minutes, and then the conjugatedcarbon/solvent slurry may be added and dispersed at, e.g., 2000 rpm for,e.g., 10 minutes to achieve a slurry viscosity within 2000-4000 cP and atotal solid content of about 30-40%. The pH of the slurry can be variedfrom acidic to basic, which may be beneficial for controlling thesolubility, conformation, or adhesion behavior of water-solublepolyelectrolytes, such as polyamic acid, carboxymethyl cellulose, orpolyacrylic acid. Ionic or non-ionic surfactants may be added tofacilitate the wetting of the insoluble components of the slurry or thesubstrates used for coating processes

The particle size and mixing times may be varied to configure theelectrode coating layer density and/or roughness. Furthermore, cathodeelectrode coating layers may be mixed in step 201, where the electrodecoating layer may comprise lithium cobalt oxide (LCO), lithium ironphosphate, lithium nickel cobalt manganese oxide (NMC), Ni-rich lithiumnickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO),lithium nickel manganese spinel, LFP, Li-rich layer cathodes, LNMO orsimilar materials or combinations thereof, mixed with carbon precursorand additive as described above for the anode electrode coating layer.

In step 203, the slurry may be coated on a substrate. In this step, theslurry may be coated onto a Polyester, polyethylene terephthalate (PET),or Mylar film at a loading of, e.g., 2-4 mg/cm² and then undergo dryingto an anode coupon with high Si content and less than 15% residualsolvent content. This may be followed by an optional calendering processin step 205, where a series of hard pressure rollers may be used tofinish the film/substrate into a smoother and denser sheet of material.

In step 207, the green film may then be removed from the PET, where theactive material may be peeled off the polymer substrate, the peelingprocess being optional for a polypropylene (PP) substrate since PP canleave ˜2% char residue upon pyrolysis. The peeling may be followed by apyrolysis step 209 where the material may be heated to 600-125° C. for1-3 hours, cut into sheets, and vacuum dried using a two-stage process(120° C. for 15 h, 220° C. for 5 h).

In step 211, the electrode material may be laminated on a currentcollector. For example, a 5-20 μm thick copper foil may be coated withpolyamide-imide with a nominal loading of, e.g., 0.2-0.6 mg/cm² (appliedas a 6 wt % varnish in NMP and dried for, e.g., 12-18 hours at, e.g.,110° C. under vacuum). The anode coupon may then be laminated on thisadhesive-coated current collector. In an example scenario, thesilicon-carbon composite film is laminated to the coated copper using aheated hydraulic press. An example lamination press process comprises30-70 seconds at 300° C. and 3000-5000 psi, thereby forming the finishedsilicon-composite electrode.

In step 213, the cell may be assessed before being subject to aformation process. The measurements may comprise impedance values,open-circuit voltage, and thickness measurements. During formation, theinitial lithiation of the anode may be performed, followed bydelithiation. Cells may be clamped during formation and/or earlycycling. The formation cycles are defined as any type ofcharge/discharge of the cell that is performed to prepare the cell forgeneral cycling and is considered part of the cell production process.Different rates of charge and discharge may be utilized in the formationsteps.

FIG. 2B is a flow diagram of a direct coating process for forming asilicon-dominant anode cell, in accordance with an example embodiment ofthe disclosure. This process comprises physically mixing the activematerial, conductive additive, and binder together, and coating itdirectly on a current collector before pyrolysis. This example processcomprises a direct coating process in which an anode or cathode slurryis directly coated on a copper foil using a binder such as CMC, SBR,PAA, Sodium Alginate, PAI, PI and mixtures and combinations thereof.

In step 221, the active material may be mixed, e.g., a binder/resin(such as PI, PAI or phenolic), solvent (such as NMP, DI water, or otherenvironmentally benign solvents or their mixtures and combinationsthereof), and conductive additives. The materials may comprise carbonnanotubes/fibers, graphene sheets, metal polymers, metals,semiconductors, and/or metal oxides, for example. Silicon powder with a1-30 μm particle size, for example, may then be dispersed in polyamicacid resin, polyamideimide, polyimide (15% solids in DI water orN-Methyl pyrrolidone (NMP)) at, e.g., 1000 rpm for, e.g., 10 minutes,and then the conjugated carbon/solvent slurry may be added and dispersedat, e.g., 2000 rpm for, e.g., 10 minutes to achieve a slurry viscositywithin 2000-4000 cP and a total solid content of about 30-40%.

Furthermore, cathode active materials may be mixed in step 221, wherethe active material may comprise lithium cobalt oxide (LCO), lithiumiron phosphate, lithium nickel cobalt manganese oxide (NMC), lithiumnickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO),lithium nickel manganese spinel, or similar materials or combinationsthereof, mixed with a binder as described above for the anode activematerial.

In step 223, the slurry may be coated on copper foil. In the directcoating process described here, an anode slurry is coated on a currentcollector with residual solvent followed by a calendering process fordensification followed by pyrolysis (˜500-800° C.) such that carbonprecursors are partially or completely converted into glassy carbon orpyrolytic carbon. Similarly, cathode active materials may be coated on afoil material, such as aluminum, for example. The active material layermay undergo drying in step 225 resulting in reduced residual solventcontent. An optional calendering process may be utilized in step 227where a series of hard pressure rollers may be used to finish thefilm/substrate into a smoother and denser sheet of material. In step227, the foil and coating proceed through a roll press for lamination.

In step 229, the active material may be pyrolyzed by heating to500-1000° C. such that carbon precursors are partially or completelyconverted into glassy carbon. Pyrolysis can be done either in roll formor after punching. If done in roll form, the punching is done after thepyrolysis process. The pyrolysis step may result in an anode activematerial having silicon content greater than or equal to 50% by weight,where the anode has been subjected to heating at or above 400 degreesCelsius. In an example scenario, the anode active material layer maycomprise 20 to 95% silicon and in yet another example scenario maycomprise 50 to 95% silicon by weight. In instances where the currentcollector foil is not pre-punched/pre-perforated, the formed electrodemay be perforated with a punching roller, for example. The punchedelectrodes may then be sandwiched with a separator and electrolyte toform a cell.

In step 233, the cell may be assessed before being subject to aformation process. The measurements may comprise impedance values,open-circuit voltage, and thickness measurements. During formation, theinitial lithiation of the anode may be performed, followed bydelithiation. Cells may be clamped during formation and/or earlycycling. The formation cycles are defined as any type ofcharge/discharge of the cell that is performed to prepare the cell forgeneral cycling and is considered part of the cell production process.Different rates of charge and discharge may be utilized in the formationsteps.

In some aspects, energy storage devices such as batteries are provided.In some embodiments, the energy storage device includes a firstelectrode and a second electrode, wherein at least one of the firstelectrode and the second electrode is a Si-based electrode. In someembodiments, the energy storage device includes a separator between thefirst electrode and the second electrode. In some embodiments, theenergy storage device includes an electrolyte, which may be provided asan electrolyte composition. In some embodiments, the energy storagedevice includes at least one electrolyte additive in the electrolytecomposition comprising a nitrogen-containing compound. In furtherembodiments, the cathode and/or anode may be created using electrodeslurries which may contain electrolyte compositions. In someembodiments, nitrogen-containing compounds are added directly toelectrode slurries to prepare directly coated electrodes. Advantages ofusing nitrogen-containing compounds include, but are not limited to,increased cycle life, increased rate capability, and power densityand/or decreased impedance increase in electrode interfaces.Specifically considering additives for cathodes, usingnitrogen-containing compounds may result in decreased transition metalion dissolution from the cathode side.

In some embodiments, the second electrode is a Si-dominant electrode. Insome embodiments, the second electrode comprises a self-supportingcomposite material film. In some embodiments, the composite materialfilm comprises greater than 0% and less than about 95% by weight ofsilicon particles, and greater than 0% and less than about 90% by weightof one or more types of carbon phases, wherein at least one of the oneor more types of carbon phases is a substantially continuous phase thatholds the composite material film together such that the siliconparticles are distributed throughout the composite material film.

In some embodiments, the battery may be capable of at least 200 cycleswith more than 80% cycle retention when cycling with a C-rate of >2 Ccycling between an upper voltage of >4V and a lower cut-off voltage of<3.3V. In other embodiments, the battery may be capable of at least 200cycles with more than 80% cycle retention when cycling with a C-rateof >2 C cycling between an upper voltage of >4V and a lower cut-offvoltage of <3.3V.

The below example devices and processes for device fabrication aregenerally described below, and the performances of lithium-ion batterieswith different electrodes, electrolytes and/or electrolyte additives maybe evaluated.

Tests may be carried out using nitrogen-containing compounds, e.g., as acathode additive. For example, 1 wt % 1,4-Phenylene Diisothiocyanate(PDIST) may be incorporated into NCM811 slurries to preparePDIST-containing NCM811 cathodes. The corresponding coin type full cellsmay be built with Si-dominant anodes and DPD-containing, or -free(control) NCM811 cathodes and may be tested using a 1 C/0.5 Ccharge/discharge cycle regime with the working voltage window of 4.2V to3.1V.

FIG. 4 . Cyclic voltammetry (CV) curves of NCM811 cathode-based coinhalf cells with 1 wt % 1,4-Phenylene Diisothiocyanate (PDIST). Thecathode used may be: (dotted line)—NCM811 Control, (solid line)—1 wt %1,4-Phenylene Diisothiocyanate (PDIST)-containing NCM811. Theelectrolyte formulation used may be 1.2 M LiPF₆ in FEC/EMC (3/7 wt %).The Si-dominant anodes contain about 80 wt % Si, 5 wt % graphite and 15wt % glassy carbon (from resin) and may be laminated on 15 μm Cu foil.The average loading is about 2-5 mg/cm². The control cathodes containabout 92 wt % NCM811, 4 wt % Super P and 4 wt % PVDF5130, and may becoated on 15 μm Al foil. The average loading may be about 20-30 mg/cm².The 1 wt % 1,4-Phenylene Diisothiocyanate (PDIST)-containing NCM811cathodes contain about 91 wt % NCM811, 1 wt % PDIST, 4 wt % Super P and4 wt % PVDF5130, and also may be coated on 15 μm Al foil with a similarloading with control. The CV measurements were carried out in thevoltage range of 2-4.3 V at a scan rate of 0.2 mV s⁻¹ using VMP3equipment.

FIG. 4 shows that there is a clear oxidation peak appearing at ˜4.0 V(vs. Li/Li+) for the cell with PDIST-free NCM811 cathode (control) inthe initial charge. This peak for 1 wt % PDIST-containing NCM811cathode-based cell shifts to ˜4.15 V (vs. Li/Li+) in the initial charge.In the following scanning cycles, the oxidation peak-related voltage isslightly higher while the reduction peaks are slightly lower for the 1wt % PDIST-containing NCM811 half cells over the control. This dataindicates that the presence of PDIST may increase the polarization andinterfacial impedance of NCM811 cathode in a voltage range of 2-4.3 V.

FIG. 5 . Capacity retention (FIG. 5A) and Normalized capacity retention(FIG. 5B) of Si-dominant anode//NCM811 cathode coin full cells. Thecathode used may be: (dotted line)—NCM811 Control, (solid line)—1 wt %1,4-Phenylene Diisothiocyanate (PDIST)-containing NCM811. TheSi-dominant anodes contain about 80 wt % Si, 5 wt % graphite and 15 wt %glassy carbon (from resin) and may be laminated on 15 μm Cu foil. Theaverage loading is about 2-5 mg/cm². The control cathodes contain about92 wt % NCM811, 4 wt % Super P and 4 wt % PVDF5130, and may be coated on15 μm Al foil. The average loading is about 20-30 mg/cm². The 1 wt %1,4-Phenylene Diisothiocyanate (PDIST)-containing NCM811 cathodescontain about 91 wt % NCM811, 1 wt % PDIST, 4 wt % Super P and 4 wt %PVDF5130, and also may be coated on 15 μm Al foil with a similar loadingwith control. The cells may be tested at 25° C.

The long-term cycling programs include: (i) At the 1st cycle, Charge at0.33 C to 4.2 V until 0.05 C, rest 5 minutes, discharge at 0.33 C to 3.1V, rest 5 minutes; and (ii) from the 2nd cycle, Charge at 1 C to 4.2 Vuntil 0.05 C, rest 5 minutes, discharge at 0.5 C to 3.1 V, rest 5minutes. After every 100 cycles, the test conditions in the 1st cyclemay be repeated.

FIG. 5 shows the 1 wt % PDIST-containing NCM811 cathode-based coin fullcells have better cycle performance than the control.

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. In other words, “xand/or y” means “one or both of x and y”. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means“one or more of x, y and z”. As utilized herein, the term “exemplary”means serving as a non-limiting example, instance, or illustration. Asutilized herein, the terms “e.g.,” and “for example” set off lists ofone or more non-limiting examples, instances, or illustrations. Asutilized herein, a battery, circuitry, or a device is “operable” toperform a function whenever the battery, circuitry, or device comprisesthe necessary hardware and code (if any is necessary) or other elementsto perform the function, regardless of whether performance of thefunction is disabled or not enabled (e.g., by a user-configurablesetting, factory trim, configuration, etc.).

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. An energy storage device comprising: a firstelectrode and a second electrode, wherein one or both of the firstelectrode and the second electrode is a Si-based electrode; a separatorbetween the first electrode and the second electrode; and an electrolytecomposition; wherein one or more of said first electrode, said secondelectrode, and said electrolyte composition comprises at least oneadditive, wherein said additive comprises a nitrogen-containingcompound; and wherein said nitrogen-containing compound is selected fromthe group consisting of (dicyanatoamino) cyanate; Phenyl Cyanate; andBisphenol A cyanate ester.
 2. The energy storage device of claim 1,wherein the second electrode is a Si-dominant electrode.
 3. The energystorage device of claim 2, wherein the Si-dominant electrode comprises:greater than 0% and less than about 95% by weight of silicon particles,and greater than 0% and less than about 90% by weight of one or moretypes of carbon phases, wherein at least one of the one or more types ofcarbon phases is a substantially continuous phase that holds theSi-dominant electrode together such that the silicon particles aredistributed throughout the Si-dominant electrode.
 4. A method of formingan energy storage device, the method comprising: forming an energystorage device comprising a cathode, an electrolyte composition, and ananode; wherein one or more of said anode, said cathode, and saidelectrolyte composition comprises at least one additive, wherein saidadditive comprises a nitrogen-containing compound; wherein one or bothof said cathode and said anode is formed using, at least, the followingsteps: said electrode material is mixed to create a slurry; saidadditive is added to said slurry; said slurry is coated on metal foil;and the coated metal foil is dried; and wherein said nitrogen-containingcompound is selected from the group consisting of (dicyanatoamino)cyanate; Phenyl Cyanate; and Bisphenol A cyanate ester.
 5. The method ofclaim 4, wherein the anode is a Si-dominant electrode.
 6. The method ofclaim 5, wherein the Si-dominant electrode comprises: greater than 0%and less than about 95% by weight of silicon particles, and greater than0% and less than about 90% by weight of one or more types of carbonphases, wherein at least one of the one or more types of carbon phasesis a substantially continuous phase that holds the Si-dominant electrodetogether such that the silicon particles are distributed throughout theSi-dominant electrode.